A network camera system may comprise a plurality of cameras which are connected in a network. The cameras in the network may capture image streams, i.e., sequences of frames of image data, which are transmitted over the network to a server. The server may e.g. request image streams from the cameras, receive the image streams, and store the image streams. The cameras typically encode, and sometimes even encrypt, the image streams prior to transmitting them over the network to the server. Thus, the server does not have access to the original image data captured by the camera, but only an encoded version of it.
For various applications, it is interesting to have a measure of the level of noise in image data. For example, the level of noise in image data may be used to define if it is day or night in the images, since the level of noise in the image data typically increases under dark light conditions.
It is known that the signal-to-noise ratio (SNR) may be used as an indicator of the level of noise in an image. However, in order to calculate the SNR, which is a measure of the level of a desired signal in relation to the level of background noise, the image data needs to be at hand. The SNR cannot therefore be applied directly on encoded image data received at the server of the network camera system without first decoding the image data.
There is thus a need for improvements.